1. Field of the Invention
The invention relates to cellular polyurethane elastomers, in particular those which can be subjected to high dynamic stresses.
2. Background Art
High requirements are placed upon the materials of cellular polyurethane elastomers applied, for example, in passenger or freight vehicle springing systems or in buffer and bumper systems subject to high dynamic stresses. Cellular polyurethane elastomers based on methylenebis-(phenyl isocyanate) (MDI) or tolylene diisocyanate (TDI) have hitherto not been able to fulfil these high requirements and have therefore so far been used for applications subject to lower dynamic stresses. The chain extending agents used in these systems are usually glycols, in particular butanediols. The resultant hard polyurethane segments have a melting range from about 180.degree. to 200.degree. C., and for cases of high dynamic or thermal stress this markedly impairs the mechanical properties of the products produced therefrom. The standard for applications involving high dynamic stresses has hitherto been cellular polyurethane elastomers based on naphthylene diisocyanate (NDI) and known as "Vulkollan". These cellular polyurethane elastomers show good behavior under dynamic stress, but they have the disadvantage that the prepolymers are not stable when stored (cf. Kunststoff Taschenbuch [Plastics Handbook], 24th edition, Carl Hanser Verlag, Munich, 1989, pp. 436ff.). The consequence for the final producer is therefore that only in-line production is possible, the prepolymer being converted immediately into the finished part. NDI-containing products also differ from industrially produced MDI products in having a significantly higher price level.